Regarding Kuwahara, the only 1980's serial number format that I've seen for them is yy mm xxxxx. It is typically stamped on the lower seat tube and was also used on the contract manufactured frames for such private label brands as Apollo, Soma and Takara, to name but three. I've also seen it used on both ATBs and road models ,so there doesn't appear to be a unique format based on frame style. Also, as previously noted, the format used on your frame has been noted on other private label brands. It seems strange that Kuwahara would have two different serial number formats for contract manufactured frames during the same period. Consequently, I'm still leaning towards your format indicating a different, unknown manufacturer.

Yes, Miyata did have a model called the Ridge Runner. It came out in 1983, so there would have been a conflict. Your frame could still be a 1984 model if the solution was to simply drop the Ridge Runner from the 1984 line and reissue the catalog but that seems a bit drastic. I would think that they would simply have re-named it. Still, that leaves the issue of the Superbe Tech rear deralleur. Due to the front pull, the chainstay cable tunnel is dedicated and therefore it's obviously not a replacement rear derailleur. Yet, we have this derailleur appearing as "New" in SunTour catalog 61 in autumn 1983, suggesting a 1984 model. The only way for it to be a 1983 derailleur would be a if it was a late introduction and wasn't catalogued until autumn 1983. Since everything is still very gray, I'd be checking for component date dates, especially the rear derailleur. Hopefully, that will lead to a decided sway, one way or the other.

Well I'd just like to sincerely thank you for taking the time to share some of your knowledge with me. I've grown very fond of 1980s Japanese bikes, and have become increasingly interested in researching the mostly undocumented history of their manufacturing. I'm in awe of the time and effort you have put in to compiling your very extensive database of serial numbers and formats.

I agree that it probably wasn't Kuwahara who made that Ridge Runner. Just found that little article interesting. I have no idea how credible that source is though, and I've never looked much into Kuwahara's bmx serial numbers.

The conflicting derailleur release date is definitely interesting. There seems to have been a lot of unexplained and undocumented changes to the Diamond Back ATBs during the early '80s, and I'd love to try and help fill in some blanks if at all possible!

I'm going to begin disassembly soon, so I'll make a note of the component date codes as I do and report back here with my findings.

The following represents the current understanding of the various serial number formats used on Centurion models marketed by Western States Imports in the USA. Serial numbers were statistically analysed and the results compared against component date codes and extant literature.

1980-1990 Japanese models:

Most Japanese models during this period use a serial number format WXYZZZZ where;

Example: N4E0283 indicates the 283 frame manufactured during the period of weeks 9-10, for the year 1984.

The letter prefix for these codes is typically 'N'. It has been suggested that this represents National, the Japanese market brand for Panasonic, which are built my Matsu****a. While the Panasonic branded models use a similar format, there is no prefix letter, nor is there a letter prefix on the Matsu****a manufactured Schwinns. This suggests the N-codes are be another manufacturer. reportedly Tano, though this is unconfirmed.

However, a number of circa 1984-1985 Centurion have turned up that match the Matsu****a format.

Miki manufactured models (circa 1975-1980)

During the late 1970s, Japan based Miki appears to have manufactured the upper end Centurion models for Western States Imports;

Example: M7C11265 is the 11,265th frame manufactured by Miki during the 3rd fortnight of 1977.

. . .

This quote: Last edited by T-Mar; 05-03-17 at 04:51 PM.

The Centurion serial numbers with the fornmat Nytxxxx,

where N = "N" frame manufacturer designation of a Japanese frame manufacturer.
y = digit, last digit in the year
t = alpha character for the manufacture time frame within the year.

It has been often stated that "t", time frame, alpha character indicates fortnight within the year.

This "fortnight" time frame never seemed right to me, as this is for a Japanese manufacturer.

For this manufacturer, where did this fortnight idea come from? I have seen no documentation to corroborate the time frame as fortnight.

This serial number format for Centurion is found from 1978 to 1989, 12 years. I have done a year by year analysis of the third character, the time frame character, for this serial number format.

The analysis shows that of the 26 letters of the alphabet, only 15 letters have been reported in serial numbers.
If the time frame is fortnight, i think you can expect that more than 15 letters would be used.

Of these 15 letters, three letters where only reported once in the 12 year history.
If you exclude these, then there are twelve letters.
All the other 12 letters were reported at least 15 time each, over the 12 years of serial numbers.

Twelve letters for twelve months?
Here is how the letters would decode as months:

A = January
B = February
D = March
E = April
G = May
H = June
K = July
L = August
M = September
N = October
P = November
S = December

This letter/month decoding is exactly the same as TI Raleigh serial numbers from 1973 to 1989.

The three letters with one reported occurance: "C", "F", "O".

This analysis is for 275 serial numbers over the 12 years, an average of almost 2 serial numbers per month.

Over the 12 years "P" is the most common letter found, November. November seems like a good time to manufacture frames to be in place for the start of the next year bicycle season.

The analysis does not include "N" serial numbers from Centurian Australia, Diamondback mountain bikes, or any of several other brand names that had frames with serial numbers with the same format. However serial numbers that I have seen from these sources have no exceptions to the month time frame letters that I have listed above.

* * * *

A similar analysis of Miki serial numbers will reveal that the third character of the serial number for time of year of manufacture is unlikly to be fortnight.

More likely to be monthly, but using a different subset of letters for month than listed above.

A = January
B = February
C = March
D = April
E = May
F = June
G = July
H = August
J = September
K = October
L = November
M = December

Looks to be a early 70's LeMans with a SN of 8X601 and the SN is located just below the seat binder bolt.

Definitely not a 1978 model , as it has the earlier decals . any thoughts? i can post picture of frame, most components are gone except for BB and Headset.

About a handful with this format and location have surfaced. In the one case where component date codes were submitted, the first numeral in the serial number did correcpond to the year of the components. Any chance that '8' might actually be '3'?

About a handful with this format and location have surfaced. In the one case where component date codes were submitted, the first numeral in the serial number did correcpond to the year of the components. Any chance that '8' might actually be '3'?

I was first considering that as the "8" or "3" stamp was light on one side, but the lighter side is the right side. the left side is a heavier strike and definitely a line there. so if it was a three there would not be the lines where i see it heavier than the right side.

I have had quite a few centurions but most in west coast however my fleet on the east coast are the following: The turbo and ironman are for sale and all stock and pristine if anyone wants pm me. I will do a full post when I have time.

I have had quite a few centurions but most in west coast however my fleet on the east coast are the following: The turbo and ironman are for sale and all stock and pristine if anyone wants pm me. I will do a full post when I have time.

I have had quite a few centurions but most in west coast however my fleet on the east coast are the following: The turbo and ironman are for sale and all stock and pristine if anyone wants pm me. I will do a full post when I have time.

hi robbie tunes. you have been so helpful in the past and i appreciate it.
the 1989 iron man master Dimensions:
bottom bracket to center of top tube - 21.82 inches
top tube/seat post area to headset 22.2 inches and
roughly a 55cm

thaks tmar. i figured it was as i remember the other turbo the red one being from 1983 if im not mistaken
turbo is 56 cm i have everything available to go back to stock except rear derailleur and brake levers. Currently set up with suntour winner pro freewheel and six speed indexed perfect. i have original bars and saddle and other parts it came with as my father is the original owner. The sungino crank and BB are better than any shimano cranksets in this era including 600 and durace imo. Hardly any effort needed to fly.

centurion carbon - all stock except fork. I have fork but I cannot seem to align it properly as if the drops are micro out of whack. I am not a veteran like you guys tho
Currently have it paired in mind with look carbon fork I have or Sakae prism silver matte similar alloy forkcenturion carbon 54 all stock I have including wheels as with all my bikes I store the bikes I have or dont use without wheels for space saving purposes. Currently this carbon is set with intention of shimano 600 sti shifters and 8 speed 600 tricolor derailleur

SN:89K4969
@T-Mar
, this doesn't seem to fit either DB or Centurion formats you have previously noted. I would guess its 89 with month k so 11-89 build? seems plausible?

Actually, that format has turned up on Centurion. I don't know the identity of the source but it's consistent with the manufacturer of the Centurion Ironman Carbons and some of the very late Centurion Prestige. However, this is the first time I've seen it on a Diamond Back. I agree with the interpretation of the format.

Actually, that format has turned up on Centurion. I don't know the identity of the source but it's consistent with the manufacturer of the Centurion Ironman Carbons and some of the very late Centurion Prestige. However, this is the first time I've seen it on a Diamond Back. I agree with the interpretation of the format.

I am very excited about picking up a Centurion Turbo in the morning and searching found this blog post:https://recoveryourstride.blogspot.c...li-equipe.html
mostly about the Equipe but there are clickable links and picks of some neat stuff. Please forgive me if this is somewhere in the 89 pages and I missed it.
Jeff